But the move isn't "enough" for Sen. Bernie Sanders of Vermont. He's calling on the retail giant to revamp its minimum wage in addition to its rules around leave.

"Walmart, which is owned by the wealthiest family in America, is not a poor company," Sanders said in a statement. "If Walmart can afford $20 billion for stock buybacks to enrich wealthy shareholders, it can afford to raise the pay of all its workers to a living wage. Walmart can and must pay all of its workers at least $15 an hour with good benefits."

Under the new system, Walmart employees will get six days of "protected PTO" for emergencies and illnesses every year. Every six months, employees will also accrue a pool of five days to use for unexpected absences. The company's vacation policy will not change.

"We're excited to introduce a new hourly attendance policy that rewards our people when they're here and provides support when they can't be," a Walmart representative told Business Insider in a statement. "These changes are based directly on feedback from our associates who wanted more flexibility to miss work when life happens, while also increasing rewards for consistently coming to work and serving our customers. Along with previous wage investments, parental leave, adoption, and other benefits, this is one more important step on our journey."

This isn't the first volley Sanders has sent Walmart's way. The senator teamed up with Rep. Ro Khanna of California last year on a bill called the Stop Walmart Act. Using stock buybacks as leverage, the bill would force companies with more than 500 workers to raise hourly wages to a minimum of $15, provide seven days of sick leave, and limit CEO compensation.

Amazon boosted its minimum wage to $15 an hour in October, a move observers noted came after Sanders had clashed with the online retailer over the amount it paid its workers.

And Sanders isn't the only one criticizing Walmart in the wake of its time-off policy announcement.

"We've been calling on Walmart to publicly commit to a healthy sick time policy that allows us to take care of ourselves and our families," Shashauna Phillips, who works at a North Carolina Walmart and is a leader of the employee-advocacy group Our Walmart, said in a statement. "Walmart is responding to our call for change with a new policy. But what they are giving with one hand, they are taking with the other — the corporation still doesn't accept doctor's notes and is even encouraging associates to come to work when they're sick with a new bonus plan."

The revamped system will give employees with good attendance the opportunity to earn some extra cash. Taking the six days of "protected PTO" won't cut employees out of the running for the quarterly bonus. But using any of the five days of time off granted every six months will cause associates to lose out on the extra money.